The invention relates to sensors and sensor systems for detecting analytes in fluids.
There is considerable interest in developing sensors that act as analogs of the mammalian olfactory system (Lundstrom et al. (1991) Nature 352:47–50; Shurmer and Gardner (1992) Sens. Act. B 8:1–11; Shurmer and Gardner (1993) Sens. Act. B 15:32). In practice, most chemical sensors suffer from some interference by responding to chemical species that are structurally or chemically similar to the desired analyte. This interference is an inevitable consequence of the “lock” being able to fit a number of imperfect “keys”. Such interferences limit the utility of such sensors to very specific situations.
Arrays of broadly cross-reactive sensors have been exploited to produce response patterns that can be used to fingerprint, classify, and in some cases quantify analytes in fluids. Such arrays have been produced incorporating sensors including heated metal oxide thin film resistors (Gardner et al. (1991) Sens. Act. B4:117–121; Gardner et al. (1992) Sens. Act. B 6:71–75), polymer sorption layers on the surfaces of acoustic wave resonators (Grate and Abraham (1991) Sens. Act. B 3:85–111; Grate et al. (1993) Anal. Chem. 65:1868–1881), arrays of electrochemical sensors (Stetter et al. (1986) Anal. Chem. 58:860–866; Stetter et al. (1990) Sens. Act. B 1:43–47; Stetter et al. (1993) Anal. Chem. Acta 284:1–11), conductive polymers or composites that consist of regions of conductors and regions of insulating organic materials (Pearce et al. (1993) Analyst 118:371–377; Shurmer et al. (1991) Sens. Act. B 4:29–33; Doleman et al. (1998) Anal. Chem. 70:2560–2654; Lonergan et al. Chem. Mater. 1996, 8:2298). Arrays of metal oxide thin film resistors, typically based on tin oxide (SnO2) films that have been coated with various catalysts, yield distinct, diagnostic responses for several vapors (Corcoran et al. (1993) Sens. Act. B 15:32–37). Surface acoustic wave resonators are extremely sensitive to both mass and acoustic impedance changes of the coatings in array elements. Attempts have also been made to construct arrays of sensors with conducting organic polymer elements that have been grown electrochemically through use of nominally identical polymer films and coatings. Moreover, Pearce et al., (1993) Analyst 118:371–377, and Gardner et al., (1994) Sensors and Actuators B 18–19:240–243 describe polypyrrole based sensor arrays for monitoring beer flavor. Shurmer (1990) U.S. Pat. No. 4,907,441, describes general sensor arrays with particular electrical circuitry. U.S. Pat. No. 4,674,320 describes a single chemoresistive sensor having a semi-conductive material selected from the group consisting of phthalocyanine, halogenated phthalocyanine and sulfonated phthalocyanine, which was used to detect a gas contaminant. Other gas sensors have been described by Dogan et al., Synth. Met. 60, 27–30 (1993) and Kukla, et al. Films. Sens. Act. B., Chemical 37, 135–140 (1996).
Sensor arrays formed from a plurality of composites that consist of regions of a conductor and regions of an insulating organic material, usually an organic polymer as described in U.S. Pat. No. 5,571,401, have sensitivities that are primarily dictated by the swelling-induced sorption of a vapor into the composite material, and analytes that sorb to similar extents produce similar swellings and therefore produce similar detected signals (Doleman, et al., (1998) Proc. Natl. Acad. Sci. U.S.A, 95, 5442–5447).
In these systems, the different responses from an analyte exposure to the array of sensors is used to identify the analyte. Other properties of the devices are designed to insure that otherwise all sensors are nominally equivalent so that the fluid containing the analyte is delivered to all sensors equally effectively—for example, at the same temperature—so that only the differences in sensors' response properties are being measured.
Although these sensor systems have some usefulness, there remains a need in the art for highly-selective sensor arrays for detecting analytes and resolving the components of complex mixtures.